Basic System Information

Hydra is a 52-node, 832-processor IBM Cluster-1600 cluster. The processors
are IBM's 1.9GHz RISC Power5+'s and these are physically packaged and organized 16
to a node. A node, a p575 node so called, is a symmetric multi-processor (SMP)
system with 16 Power5+ processors and a shared memory of 32 gigabytes. Of these
32 gigabytes only 25 are available for user processing. Keep that in
mind when setting batch job memory limits. The 52 nodes are further organized
and housed into five physical frames or racks, stacked ten nodes to a rack for
frames 1-4 and twelve for frame5. In all, only 48 nodes are interconnected via
the HPS, the IBM High-Performance communication Switch: all 40 nodes in frames 1-4
and only 8 nodes in frame5. All 52 nodes are interconnected with gigabit
ethernet. The cluster uses the HPS for parallel processing and other
communication between the 48 nodes. Each of the 48 p575 nodes connects to the
HPS network using two adapters. Each of these in effect attaches to one of the
two available subnetworks via which HPS routes a message packet to another (of
the 48) node.

Fig. 1: Power5+ Dual Core Chip. The Basic Building Block

Fig. 2: The p5 575 Node at a Glance

Fig. 3: p5 575 Internal Schematic

Fig. 4: Node Roles as Configured on HYDRA

Fig. 5: The DDN Disk Raid Array connections to Hydra

Advanced Hardware and Software Architecture

You will find a much more detailed and informative description of a number
of advanced hardware and software architecture issues for the entire Hydra cluster in the
Advanced Cluster Architecture section of the
user guide.

Login Nodes: hydra1.tamu.edu and hydra2.tamu.edu

The staff has configured the naming of the nodes to reflect their physical
location in the five racks. In the first four racks there are ten nodes. A fifth
rack, added in February 2009, has 12 nodes. A node name consists of a four- or a five-character
string, f[1-5]n[1-10/12]. For example, f3n9, refers to the 9th node in rack 3,
f5n12 is node 12 in rack 5, etc. Node numbers increase from the (physical) bottom
up, 1-10/12. Two of the 48 HPS-interconnected nodes, f1n9 and
f1n10, are allocated to
interactive processing. Logins are enabled only to those two nodes.
The internet host nanes of f1n9 and f1n10 are hydra1 and hydra2, respectively.
The rest of the nodes are only accessible by the LoadLeveler, the
batch facility. You can view this list of nodes using the LoadLeveler command,
listnodes (llstatus -f %n will also work). Even more useful for tracking batch
jobs is the listnodeusage command which lists the nodes that specific jobs
run on. A sample listing follows.